The origins of the label are debated. The redoubtableDamrong Rajanubhab, an eminent Thai historian and prince, asserted that the Siamese were "following the example of the Indian (sic) who called all European 'Farengi'" (the similarity to the term Ferengi is no doubt completely accidental).

In Thailand some Thai told me, as they may have done my colleague, that the label is a Thai corruption of "French", though current Thai pronunciation of that word is more like "franset". (Some Thai letters change their sound depending on their position; the "s" letters are some of these. At the end of a word, "s" letters are pronounced "t" or "d". Foreign words often get assimilated into Thai pronounciation, so that the "farangais" Teiresias refers to usually comes out more like "farangait" or, as I've rendered it, "franset".)

Some argue that the Siamese took the label from Muslims, who referred to Europeans as "Franks". This latter explanation seems to me the most likely, given the integration of Muslims into the Ayuthayan Siamese polity since the fifteenth or sixteenth centuries, and the Thai tendency to drop the final hard consonant from a foreign-derived word.

By the way, farang also means guava in Thai, so a western person consuming that fruit is always good for a giggle.